Electric furnace.



Patented Sept. 4, |900.'

H. c. msnm.' ELECTRIC' Fu-RNAGE. (Applicatinn led May 13, 1.899.)

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m: wams Pneus co, Hom-umu.. wAsHuxcTuN, D4 c UNITED STATES lPMENT OFFICE.

HENRY C. MCBRAIR, OF MIDDLETOVVN, NEW YORK.

ELECTRIC FU RNACE.

SPECIFICATION forming part of Letters Patent No. 657,202, dated September 4, 1900. application nea my 1s, 1899. sain No. 716.780. (Nomoaei.)

T0 all` whom, t may con/037%: 1

Be it known that l, HENRY C. MCBRAIR, a citizen of the United States, and a resident of the city of Middletown, Orange county, New York, have invented certain new and useful .Improvements in Electric Furnaces, of which the following is a specification.

My invention relates to a class of electrically-heated furnaces used by dental surgeons principally for firing porcelain; and it consists of an improved electrical connection between the two separable parts of the furnace, such that the electrical current is not interrupted or changed in either part when the furnace is opened, and, further, in a certain shape of the two separable parts, such that the case may be exposed to view by a small opening of the parts and also may receive the direct radiation of heat from the upper part when that part is slightly raised.

l-litherto electrically-heated furnaces have been so constructed that the electrical connections between the lower and upper coils are made through two vertical metallic springs secured to the base in front of the furnace and pressing against contact-points on the upper part. These contact-springs are in the way of the operator when he is examining the case which is being fired in the furnace, and, worse than this, since they make contact on the front of the lid or upper part this contact is broken by a very small elevation of the upper part. This interruption of the current in the upper circuit, made necessary by the present construction, every time the upper part is elevated is objectionable, be'- cause where a dynamo-current is used in the circuits an arc is likely 'to be struck, which soon ruins both the springs and contactpoints, and the absence of caloric effect in the uppercoils permits a dangerously-sudden cooling of the case by the admitted cjool air, which may cause surface cracks, and also the increase of the current in the lower coil, caused by opening the circuit in the upper coil, which is usually in parallel connect-ionwith it, sometimes is sufficient to fuse and destroy this coil. Furthermore, in these furnaces, as at present constructed the upper and lower parts meet on a horizontal plane, and the case is placed in a cavity, about one-half of which is formed in the lower part. Hence a considerable opening of the parts is needed to inspect the case. This open ing is likely to produce a too-sudden cooling of the case, as referred to. In order to avoid the frequent opening of the furnace for inspection,it is usual to provide a peep-hole through which the operator can observe the progress of the work. This opening is a source of constant loss of heat and at best only allows the inspection of a limited area of the case. I have the upper and lower parts of my improved furnace meet on an inclined plane which diagonally intersects the case as it lies in the lower cavity. l

In the several drawings similar characters refer to similar parts.

Figure lis a side elevation of my improved furnace. Fig. 2 is a vertical cross-section on the line m Iy of Fig. 4. Fig. 3'is a rear elevation. Fig. l is a plan view from below. Fig. 5 is a vertical cross-section of one of the hinges, and Fig. 6 is a diagram of the electric circuits.

The four principal structural parts of the furnace are the upper part A, the lower part B, the base C, and the refractory lining D. The upper part A may turn through an angle of, say, one hundred and twenty degrees about the horizontal hinge-joint d b d b. The npper and lower parts A and B together form a hollow vmetallic cylinder with closed ends. They meet on an inclined plane Z, which intersects the plane of the'base C in a line in front of the lower part B. The base G is preferably of metal and is the foundation to which the lower part B, the binding-posts I and J, and the contact-springs K and L are attached.

The interior of the parts A and B is lined withrefractory material D D, preferably fireclay, which is a non-conductor or a poor conductor of electricity. Within this refractory lining is a centrally-located cavity consisting of two parts E and F, the one in the upper part A and the other in the lower part B. This cavity is usually cylindrical in shape, with the ends of the cylinder forming horizontal upper and lower walls. This cavity is so placed that the inclined plane Z cuts through it at or near its lower front corner. The upper, lower, and surrounding walls of cavities E and F have embeddedin them, slightly beneath the surface, a number of convolutions IOO of platinum wire in two heating-circuits G and H in the upper and lower parts of the cavities E and F, respectively. The upper heating-circuit G pierces the walls o't the upper partA through the lava insulating-bushings q and q', Fig. 3, and theends g and g of this circuit are electrically connected to the pins T and rl, respectively. The lower heating-circuit II in the lower part B pierces the walls of this part and the base C through the lava insulating-bushings O and O, Fig. 4, and the ends 71. and h are electrically connected to the insulated conductors m and n. (See Fig.` 4.) Conductor m is electrically connected to contact-spring K and binding-post I, Vwhile conductor n is electrically connected io contact-spring L and binding-post J. Binding-posts I and J and contact-springs K and L are electrically insulated from the base C by the lava bushings and washers j and 7a Z, respectively. Contact-springs K and L are rigidly attached to the base C at their lower ends and make electric contact with the pins T and T', respectively.

The two hinges a Z) and c' Z2' are of similar construction. Fig. 5 shows a vertical crosssection, on a larger scale, of the hinge formed of ear cd, connected to upper part A, and ear ZJ', connected to lower part B. A horizontal hole, of varying diameter, is bored through both ears. This hole is small when passing through ear b and is tapped with a screwthread in this ear. The hole continues to be small through about one-half of ear a' nearest to b and then is considerably increased in diameter where it passes through the remaining part of ear a. A screw VV, with the thread removed from a portion of the end, is screwed into the threaded hole in ear b, and its smooth end enters the small hole in ear a. On the smooth end of this screw lV/ the binge turns. A lava insulating-bushing S is inserted into the larger part ol' the hole in ear a. Into the bushing S the metal pin T is placed. Aga-inst this pin T the contactspring L presses.

As previously stated, the end g of the upper heating-circuit G is electrically connected to pin T, and the end 7L of the lower heating-circuitH is electrically connected through conductora to the lower end of contact-spring L and also to binding-post J. Hence the spring L completes the electrical connection 0l one end of the lower l'ieating-conductor II and the binding-post J with one end of the upper heating-conductor G through contactpin T. Similarly spring K completes the electrical connection of .the other end of the lower heating-cond uctor and the binding-post- I with the other end of the upper heatingconductor through contact-pin T. New as the electrical connections or contact between contact-springs K and L and contact-pins T and T are in no way interfered with by the movement of upper part A on hinges a l) and c 7J it follows that the electrical connections throughout the furnace, as described, are in no way disturbed or changed by opening or closing the furnace.

In the diagram of the electric circuits illustrated by Fig. G, U is the source of electrical energy. V is a rheostat. l and J are the two insulated binding-posts. G and Il are the upper and lower platinum heating-eircuits. K and L are the two contact-springs, and T and T are the two contact-pins. It will be seen that the electric current on leaving one pole of the battery passes through' as many resistance-coils ot' the rheostat as may be in circuit, enters the furnace through binding-post I, dividing between the lower and upper heatiiig-conductorsJ and returns to the other pole of the battery through binding-post J; but in order to reach the upper heating-conductor G the current enters through contact` spring K and pin T and leaves through pin T and spring` L. The direction ot the current through the furnace is not important.

In Fig. l the position of the upper part A is shown in dotted lines when the furnace is open. Here it will be observed, as previously stated, that the raising or closing of the upper part does not in any way interfere with the electrical connections between the circuits in the upper and lower parts.

The inclination of the plane Z, in which the two parts A and B meet, accomplishes very important results. It makes the bottom of the cavity F accessible by a slight raising of the upper part A. It permits of the observation of either side of the case along a diagonal line by a slight raising of the upper part, and it further permits of the direct radiation of the heat from the walls of the upper cavity upon the case in the lower cavity when the upper part A is raised through a few degrees. Thus it is seen that the inclined opening, in connection with the permanency of the electrical connections between the upper and lower partsJ obviates the use of the wasteful peep-hole and other equally or more objectionable features of the present construction.

I do not limit myself to the precise construction and arrangement here shown and described, but claim the right to the various obvious methods of carrying out the principles of my invention.

The connections illustrated place the upper and lower heating-circuits in parallel with each other. In my larger type of furnace I subdivide the heating-circuits into several circuits connected in parallel. In a smaller type of furnace I connect the upper and lower heating-circuits in series-an arrangement easily carried out with my permanent connections between these circuits.

I am aware that in electrically-heated .tur-- naces it is not new to embed the heating-circuits in refractory non-conducting material, nor is it new to use a controllable electric IIO current in such a furnace nor to make the furnace in two parts hinged together; but

What I claim as my invention, and desire to secure by Letters Patent, is-

1. In an electrically-heated furnace the combination of two hinged parts, an electric heating-circuit in each part, and insulated electric connections between said circuits, said connections consisting of contact parts which move on each other, when the hinged parts are operated, and maintain a continuous electrical connection between said circuits.

2. In an electrically-heated furnace', the combination of two hinged parts; a refractory, non-conducting lining in each part, an

electric heating-circuitin each part embedded in said lining; an internal cavity in each of said parts, said heating-circuits lying near the sides of said cavities; and insulated electric connections between said circuits, said connections consisting of contact parts which move on each other, when the hinged parts are operated, and maintain a continuous elecf trical connection between said electric circuits.

3. In an electrically-heated furnace, theL combination of two parts that are connected in a horizontal hinged joint and meet in an inclined plane parallel to said horizontal hinged joint; an electric heating-circuit in each of said parts; and` means for maintaining a continuous electrical connection between said heating-circuits when one of said parts is turned on said hinged joint.

Al. In an electrically-heated furnace, the combination of two parts that are connected with a horizontal hinged joint, and meet in an inclined plane, parallel to said horizontal hinged joint; an electric heating-circuit in each of said parts; means for maintaining a continuous electrical connection between said heating-circuits when one of said parts is turned on said hinged joint; and a controllable source of electricity for continuously supplying an electric current to both of said heating-circuits, whether said parts are close together or whether they are separated by the turning of one of the said parts on said hinges.

5. In an electrically-heated furnace, the combination of two hinged parts; an insulated electric circuit in each part; and insulated, electrical contact parts, on or near the hinges connecting said parts together, the points, or surfaces, of contact of said electrical contact parts movable on each other when said hinged parts are operated, thereby maintaining a continuous electrical connection between said electric circuits whether said furnace is open or closed.

6. In an electrically-heated furnace, the combination of an upper and lower part; two hinges connecting said parts together; abushing of refractory and non-electrical conducting material in each of said hinges; a metallic pin in each of said bushings; an insulated electric conductor in each of said parts; an electrical connection between each of said pins and one end of said electric circuit in said upper part; a metallic spring pressing against each of said pins; an electrical connection between each of said springs and one end of the electric conductor in said lower part; and a controllable source of electricity to supply an electric current to said electric conductors, substantially as described.

7. In an electric furnace having hinged parts the combination of an insulated elec.- tric circuit, a portion of which lies in each of said hinged parts; and electrically-insulated points or surfaces of contact, forming a continuous electrical connection between the portions of said electric circuit and movable on each other when the said hinged parts are operated.

In testimony that I claim the foregoing as my invention I have signed my name, in presence of two witnesses, this 4th day of May, 1899.

HENRY C. MCBRAIR.

Witnesses:

Jol-IN MCWILLIAMs, E. M. LAIN. 

